αA- and αB-crystallins are molecular chaperones expressed at low levels in lens epithelial cells, and their expression increases dramatically during differentiation to lens fibers. However, the functions of αA- and αB-crystallins in lens epithelial cells have not been studied in detail. In this study, the relative ability of αA- and αB-crystallin, in protecting lens epithelial cells from apoptotic cell death was determined. The introduction of aA-crystallin in the transformed human lens epithelial (HLE) B-3 lens epithelial cell line (which expresses low endogenous levels of αB-crystallin) led to a nearly complete protection of cell death induced by staurosporine, Fas monoclonal antibody, or the cytokine tumor necrosis factor a. To further study the relative protective activities of αA- and αB-crystallins, we created a cell line derived from αA-/-αB-/- double knockout mouse lens epithelia by infecting primary cells with Ad12-SV40 hybrid virus. The transformed cell line αAαBKO1 derived from αA/αB double knockout cells was transfected with αA- or αB-crystallin cDNA contained in pCIneo mammalian expression vector. Cells expressing different amounts of either αA-crystallin or αB-crystallin were isolated. The ability of αA- or αB-crystallin to confer protection from apoptotic cell death was determined by annexin labeling and flow cytometry of staurosporine- or UVA- treated cells. The results indicate that the anti-apoptotic activity of αA-crystallin was two to three-fold higher than that of αB-crystallin. Our work suggests that comparing the in vitro annexin labeling of lens epithelial cells is an effective way to measure the protective activity of αA- and αB-crystallin. Since the expression of αA-crystallin is largely restricted to the lens, its greater protective effect against apoptosis suggests that it may play a significant role in protecting lens epithelial cells from stress.